Well..... the anime didn't actually correct for this very well. Keep in mind the Utakata stuff is in fact filler; so Naruto won't remember him. Here's the thing, the anime did follow what Diedara said by explaining that prior to Gaara, only 2 jins had been captured. But they screwed that equilibrium up when they got to the 2 tail. Remember how the anime sealed 3 and 4 at the same time when the manga sealed 2 and 3 at the same time? Well when they sealed the 2 tail in the anime, there were 5 total eyes filled in the statue, not 4 as it should have been if they expected to make the Utakata filler. In fact, after sealing the 3 and 4 tails, the statue showed 7/9 eyes opened implying they were staying consistent with the manga. So when the sealed the 6 tails..... one eye slot that used to be filled suddenly was available for sealing and opened a second time.....
So in reality, the anime makers were never told that Kishi planned for them to use the Utakata filler and in reality, this manga mistake screwed the anime up far more than it screwed the manga up. Its crazy to think so, but it did.
Naw. Most of the mistakes we see are quick decisions made by one or more people involved in the manga that lead to something being missed. I mean the fact that the hydra had 9 heads is actually hard to see. If you don't look real close then you wouldn't notice. So someone who drew it up could have easily drawn one extra head by mistake after having hidden one of the heads behind another.
As for the obvious mistakes about the number of Jins captured prior to part two and the number of people that Oro took possession of up to that point, these are things that Kishi had to make decisions on very early and could suddenly change his mind later on. But the Jins mistake is no small matter. IMO, it is clear that Kishi made a drastic decision to change the remaining number of jins for some reason. Perhaps he decided to cut the number of jins down by one since he thought the story might get too long? Idk for certain but clearly he changed his mind on the matter later on.